Diagram of the targeting strategy to generate the Mgp-Cre knock-in allele. (A) The targeting vector consists of homology arms of 1972 promoter bp, exon 1, intron 1, exon 2, intron 2, exon 3, intron 3, exon 4, and of 3022 bp of 3′ genomic sequences (total 8.3 kb). Sequences containing the IRES-Cre-FRT-flanked neomycin resistance gene cassette were inserted between the Mgp STOP signal and the 3′UTR. (B, C) Targeted locus before and after the action of the FLP recombinase. (D) Final targeted locus after removing the FLP recombinase gene. The arrowheads denote the primer pairs used for genotyping (primer sequences in methods). (E) PCR was performed with the indicated primers pairs on genomic DNA from the knock-in lines carrying the corresponding alleles. pA, poly-adenylation sequence; KI, knock-in. All amplimers match the expected sizes.